The invention relates to an Automatic Manual Transmission (AMT) and the control of such an AMT. In particular the invention relates to a map for control of the gear selection in such an AMT.
The use of Automatic Manual Transmissions (AMT) has been increasingly common during the last years and is today a common feature in many vehicles. The inclusion of an automatic gear shift selection has made the driving more easily for a driver who instead of putting an effort on selecting the right gear may concentrate on the driving and the surrounding traffic. In particular for heavy duty vehicles, an automatic shift system such as AMT has been of a great value.
In order to control the automatic system, a number of control strategies and shift pattern maps have been suggested. In U.S. Pat. No. 5,067,374 and U.S. Pat. No. 4,841,815 is described the use of fuzzy logic in order to select a gear. U.S. Pat. No. 4,922,428 describes a learning system for improving a gear selection pattern. US 2007/0254774 describes a system for selecting between a manual shift mode and an automatic shift mode or different automatic shift modes. It is also known to use different gear shift patterns depending on different parameters and this is for exampled disclosed in U.S. Pat. No. 6,519,520; US 2006/0155447; U.S. Pat. No. 5,911,771 or U.S. Pat. No. 6,182,000.
Even though the above documents provides different systems for control of an automatic transmission, there are still certain desires not fulfilled concerning these kind of systems to perform well over a wide variety of operating conditions. Hence, it is desirable to adapt a vehicle provided with an AMT to work in a satisfactorily way under an increased diversity of conditions.
The present invention provides, according to an aspect thereof, a new powertrain system for a vehicle and a method for improved control of an Automatic Manual Transmission (AMT). Hence, an aspect of the invention relates to a powertrain for a vehicle and a system according to an aspect of the invention that comprises                an automated master clutch,        a stepped gearbox and        a control unit adapted to control said master clutch and said stepped gearbox.        
The control unit is programmed to generate a control signal indicating a desired gear selection. The control unit comprises at least two different sets of gear selection control algorithms for generating the gear selection control signal and the different control algorithms are programmed to generate different gear selection control signals based on input data, i.e. the same input data will make the gear selection control signal differ for at least one state of the input parameters. The control unit is further connected to a gear selection control algorithm selector which indicates which set of gear selection control algorithm that is to be used by the control unit. Among the at least two different gear selection control algorithms are at least a first gear selection control algorithm intended to be used when driving said vehicle in a normal mode corresponding to the conditions on an ordinary road, e.g. this is the control strategy normally used by the vehicle if not any particular strategy or program is selected.
According to the present invention, the gear selection control algorithms comprises a second gear selection control algorithm intended to be used when driving said vehicle in a soft surface mode. By the term “soft surface mode” is for example included when the vehicle is driving in sand, e.g. in the desert. There may of course be other similar conditions, at least with respect to the properties or conditions for the powertrain and the wheels, when this mode also may be used, e.g. driving in loose snow or wet mud. Hence, this mode is intended to include different kind of conditions when there is a soft surface, e.g. a surface comprising some kind of particulate matter or loose material, such that the grip for the traction wheels is lower than usual and, likewise, the rolling property is also lower than usual due to the inherent property of a loose material to let the wheels “sink” into the surface and while the surface material will not keep together when a force is transmitted to the surface, e.g. from the traction wheels. Hence, there is a reason for changing the control system or gear shift control signals for different conditions since the normal control modes does not satisfactorily manage the powertrain system in certain, extreme conditions. For example, when a vehicle, e.g. a heavy duty vehicle provided with an AMT, is driving in the desert and is climbing a hill, the running resistance is far more than when climbing for example an equally inclined hill having an asphalt surface. If no adaptation is made due to the changed condition, the vehicle will use a too high gear and will not be able to climb the hill as desired. When the gear is shifted down, it is very likely that the wheels start to slip, at least for a short while since the loose sand easily allow a spin and as a result of this, the gearbox may change up again to the undesired, higher gear. This scenario may occur several times and the vehicle will essentially not move forward and, if the hill is steep enough, probably stop completely. Hence, there is a need for another shift strategy mode adapted to these conditions in order to allow a vehicle provided with an AMT to travel safe and smooth in an increased variety of environments.
In one embodiment of an aspect of the invention, the second gear selection control algorithm is programmed to perform a shift to a selected higher gear at a higher engine speed than when the normal mode gear selection control algorithm is used. If for example a gear shift normally is predicted and performed at for instance 1600 rpm, the level for shifting may be raised to 1900 rpm.
According to still another embodiment, which may be used alone or in combination with the foregoing embodiment, the gear shift may include smaller steps. If for example in a gearbox equipped with 12 forward gears the gears are shifted stepwise using the gear steps 2-5-8-10-11-12 according to a normal gear shifting mode when shifting up from gear step 2 to 12, the gear steps used when driving in the soft surface mode may for example be 2-4-6-8-9-10-11-12 when using the soft surface mode. Hence, more gear shifts are included in the soft surface gear shift pattern when shifting from the lowest possible gear to the highest possible gear compared to the normal gear shifting pattern and when in both said gear shifting patterns the lowest and highest gear are the same. In the example above, two extra gear shifts are used in the soft surface mode compared to the normal mode when shifting from the 2nd to the 12th gear.
At a first glance, the suggested shift pattern may seem to be similar to shift patterns for a sport mode or the like for a vehicle. However, there are some basic differences between the soft surface mode and such a sport mode. In the soft surface mode the shift pattern is optimized to be able to provide a sufficiently high driving force in order to avoid that the vehicle stops or needs to shift back to a lower gear. In the sport mode, the vehicle is optimized to change gears so as to provide optimal acceleration. Furthermore, the intended use of this soft surface shift mode pattern is directed to heavy vehicles and utility vehicles such as trucks and the like vehicles which have a highly complex powertrain and gearbox comprising a split gearing, a main gearbox and a range gear which is controlled by an ECU to automatically shift the gears. A sport mode is usually provided in standard vehicles such as cars having a different gearbox and a different intended use as a family vehicle.
In still another embodiment, the gear selection control algorithm may also be dependent on the steering angle such that there is an increased engine speed limit for changing a gear when there is an increased steering wheel angle. In particular, an up shift may not be allowed when the steering angle is above a predefined limit. Another possibility is to demand a downshift if the steering angle is above a certain limit. Hence, the steering angle may very well be used as one of several input parameters which together define the soft surface shift control strategy. For example a steering angle corresponding to a turning radius of 100 meters can give zero increase of the engine speed limit for changing a gear. Whereas a steering angle corresponding to a turning radius of 20 meters can give 200 rpm increase of the engine speed limit for changing a gear.
According to one embodiment, the gear selection control algorithm selector is operated manually such that said second gear selection control algorithm, i.e. the soft surface mode, may be manually selected. It may of course also be an automatic turn on/off feature depending on exterior conditions and vehicle features or a combination of these systems, e.g. an auto select mode or a mode where the driver intentionally selects which gear shift or gear selection mode that is to be used.
The control unit may be connected to or comprise a look up table or a mathematical formula to be used for generating the gear selection control signal.
Furthermore, according to a further embodiment of an aspect of the invention, the system may comprise also the feature of estimating or computing a travel resistance value from data retrieved from relevant sensors known in the art such that a control system in the vehicle may predict when the powertrain shall be controlled by the second gear selection control algorithm, i.e. the soft surface mode, and when it shall be controlled by another gear selection control algorithm, e.g. a normal mode. The selection of which mode to be selected may be made by setting a level of the travel resistance above which the soft surface mode will be selected if the travel resistance has been above that level for a certain time. The travel resistance can for example be estimated by measuring tractive force (amount of injected fuel or torque sensor), vehicle mass and vehicle acceleration and using the known equation Ftractive−Fresistance=m*a, where Ftractive is tractive force and Fresistance is travel resistance, m is vehicle mass and a is vehicle acceleration. The estimated value for the travel resistance can be compared with a value for a climbing force, which can be estimated using a road inclination sensor, in order to obtain a better value for the travel resistance.
According to still another embodiment, which may be used together with the earlier embodiments, quicker torque ramps at the gear shifts are performed when the powertrain is controlled according to the second gear selection control algorithm than when controlled by the first gear selection control algorithm. This feature may be used since the surface, e.g. loose sand, will not grip to hard and even though a gear is engaged rather quickly, the soft surface will allow a certain slip and there will be a rather smooth reaction force working on the powertrain and the gearbox. The quicker torque ramps will reduce the shift time, i.e. the time when there is an interruption of power to the traction wheels, and will therefore provide a better chance to succeed when performing an upshift in steep conditions.
The soft surface mode shall also allow a rather large slip before shifting down and the soft surface mode shall not be provided with features reacting to a slip or at least allow a slip of the wheels which is far more than is allowed in a normal mode. This is due to the fact that it is expected that the wheels will slip when there is a soft surface.
The method according to an aspect of the invention is a method for controlling a powertrain for a vehicle. The method is characterized in the steps of:                registering a road condition;        if said registered road condition corresponds to normal road conditions then a first gear selection control algorithm is used intended for driving said vehicle in a normal mode corresponding to the conditions on an ordinary road;        if said registered road condition corresponds to soft surface road conditions then a second gear selection control algorithm is used intended for driving said vehicle in a soft surface mode corresponding to the conditions on an soft surface road.        
Further embodiments of the method correspond to said embodiments of the power train system.
The invention is further directed, according to an aspect thereof, to a vehicle comprising such a powertrain as described above. In particular, this powertrain is suitable for a heavy duty vehicle such as a truck.
One embodiment of an aspect of the invention comprises said powertrain a split gearbox, a main gearbox and a range gear.
In addition, the invention is directed, according to an aspect thereof, to a computer program, computer program product and a storage medium to be used with a computer for executing the gear shift selection according to the invention.